As mobile devices have been increasingly developed, and the demand of such mobile devices has increased, the demand of batteries has also sharply increased as an energy source for the mobile devices. As a result, much research on batteries satisfying various needs has been carried out.
In terms of the shape of the batteries, the demand of prismatic secondary batteries or pouch-shaped secondary batteries, which are thin enough to be applied to products, such as mobile phones, is very high. In terms of the material for the batteries, the demand of lithium secondary batteries, such as lithium ion batteries and lithium ion polymer batteries, having high energy density, high discharge voltage, and high output stability, is very high.
One of problems to be principally solved in connection with the secondary batteries is to improve the safety of the secondary batteries. For example, the lithium secondary batteries may explode due to the increase of temperature and pressure in the batteries, which may be caused by abnormal operations of the batteries, such as internal short circuits, overcharge exceeding allowed current and voltage, exposure to high temperature, or deformation due to falling or external impacts.
Among secondary batteries is a secondary battery including a stacking type electrode assembly in which the structural strength of the stacking type electrode assembly is low, and therefore, the secondary battery has high possibility that internal short circuits will occur due to falling or external impacts.
FIG. 1 is an exploded perspective view illustrating the structure of a pouch-shaped secondary battery including a general stacking type electrode assembly.
Referring to FIG. 1, a pouch-shaped secondary battery 100 is constructed in a structure in which an electrode assembly 300 including cathodes and anodes arranged such that cathode taps and anode taps protrude while being opposite to each other and separators disposed respectively between the cathodes and the anodes is mounted in a battery case such that two electrode leads 301 and 302 electrically connected to the cathode taps and the anode taps, respectively, are exposed to the outside.
The battery case 200 is made of a soft wrapping material, such as an aluminum laminate sheet. The battery case 200 includes a lower case having a hollow receiving part for receiving the electrode assembly 300 and an upper case. The battery case 200 may be formed using a mold constructed in a shape corresponding to the electrode assembly 300.
The cathode taps and the anode taps of the stacking type electrode assembly 300 are coupled to the electrode leads 301 and 302 by welding. To the upper and lower surfaces of the electrode leads 301 and 302 are attached insulation film 400 for securing the electrical insulation and sealability between the battery case 200 and the electrode leads 301 and 302.
However, the pouch-shaped secondary battery 100 has a problem in that the battery case 200 is made of a soft wrapping material having low strength, and therefore, the battery case is easily deformed when the secondary battery falls or external impacts are applied to the secondary battery. Furthermore, in the stacking electrode assembly 300, internal short circuits may occur due to the movement of electrodes about the separators due to the falling or the external impacts. Especially, the falling or vibration of the secondary battery frequently occurs during the use of the secondary battery. Consequently, there is high necessity of a technology for more efficiently securing the safety of the secondary battery.
In order to solve the above-mentioned problems, Korean Utility Model Registration No. 0355114 discloses a technology for mounting an electrode plate group (electrode assembly) including cathodes, anodes, and separators in a battery case and inserting insulative holding pins through through-holes formed in the electrode assembly and the battery case so as to restrain the movement of cathodes and anodes. However, this technology essentially requires that the battery case be stiff because the holding pins are inserted through the through-holes of the battery case. Also, an electrolyte may leak from the battery case through the through-holes of the battery case. Furthermore, when the holding pins are inserted through the through-holes of the electrode assembly, the cathodes and the anodes may be brought into contact with each other in the through-holes, and therefore, internal short circuits may occur.
In addition, Japanese Patent Application Publication No. 2000-030670 discloses a secondary battery in which a through-hole is formed in the middle of an electrode assembly, and an insulative connecting member to be inserted though the through-hole is formed at a plate member which is mounted to one major surface of the electrode assembly. However, this technology requires the plate member as an additional mounting member. Furthermore, when the insulative connecting member is inserted through the through-hole, internal short circuits may occur.
Even though having a somewhat different object, Japanese Patent Application Publication No. 2002-246007 discloses a technology for mounting current collecting terminals for electrical connection to one-side ends of cathodes and anodes of an electrode assembly, drilling holes in the electrodes, inserting conductive pins through the holes such that the conductive pins are connected to the current collecting terminals, which is distinguished from a conventional technology for accomplishing electrical connection using electrode taps. However, this technology has problems in that the manufacturing process is very complicated, the total size of the secondary battery is inevitably increased, and the change in volume of the secondary battery during the charge and discharge of the secondary battery is not restrained, although the secondary battery is constructed in a structure in which the through-holes are formed in a part of the electrode assembly and the additional members are inserted through the through-holes.